A circadian rhythm paradigm involving mice is described for the simultaneous, quantitative study of 1) wakefulness-sleep (polygraphically defined), 2) activity-inactivity (wheel running), 3) brain temperature (from an implanted thermister), 4) performance (bar press for food), and 5) electroencephalographic power spectra (on-line computer analysis). The temporal inter-relationships of these measures will be detailed under entrained and free-running conditions, with special attention to performance changes in association with the spontaneously occurring damping abnormalities in wakefulness-sleep cycles that occur in long, free runs.